Continuous process for recovery of magnesium



1951 F. J. HANSGIRG CONTINUOUS PROCESS FOR RECOVERY OF MAGNESIUM 3Sheets-Sheet 1 Filed June 26, 1945 Oct. 9, 1951 F. J. HANSGIRG 2,570,232

CONTINUOUS PROCESS FOR RECOVERY OF MAGNESIUM Filed June 26, 1945 3Sheets-Sheet 2 Patented Oct. 9, 195.1

CONTINUOUS PROCESS FOR RECGVERY OF MAGNESIUM Fritz J. Hansgirg, BlackMountain, N. 0., assignor to North Carolina Magnesium DevelopmentCorporation, Asheville, N. 0., a corporation of North CarolinaApplication June 26, 1945, Serial No. 601,701

6 Claims.

This invention relates to the production of metallic magnesium, and hasfor its general object the provision of novel methods for producingmagnesium by a substantially continuous process.

I In thermal reduction processes, as pursued at the present time, eitherby reduction of raw material containing magnesium oxide by means ofcalcium carbide, ferro-silicon, silicon carbide, or similar .reducingagents, or in the distillation of magnesum dust which has been recoveredby a thermal reduction process, batch methods are employed. In all ofthese processes, the problem involves heating the starting materials totemperatures of between l000 and 1300 C. in a high vacuum; andin thecase of the recovery of magnesium from dust produced by the thermalreduction method, temperatures of from 600 to 750 C. are necessary,while also maintaining high vacuum conditions. The necessity forintroducing the raw materials into high vacuum and the fact thatmagnesium at its melting point already has a vapor pressure of 2.5 mm.of mercury (absolute pressure), makes it exceedingly difilcult toprovide a continuous process. Several proposals have been made lookingtoward the solution of the problem of continuous distillation, but thedifiiculties in providing suitable apparatus have been consideredinsuperable and the simpler arrangements for batch processes have beenconsidered more economical and practical.

It is therefore one of the principal aims of the present invention toprovide methods for carrying on the thermal reduction of magnesiumcompounds in a substantially continuous, or semi-continuous way. That isto say, the apparatus in which the process is carried on does not haveto be opened to the atmosphere for the introduction of the startingmaterials nor for the removal of the magnesium produced or the wastematerial, the introduction and withdrawal of the materials and theirtransfer from one stage to the other being preferably automaticallyeffected according to a time cycle adjusted for the specific rawmaterials and reducing agents employed.

In all of the above mentioned reduction process, a vacuum of at least 1mm. to 0.1 mm. of mercury (absolute pressure) is necessary. It istherefore essential that the magnesium be condensed in the solid statesince only solid magnesium has a vapor pressure below the degree ofvacuum mentioned.

a It has previously been proposed, in the distil- 2 lation of magnesiumdust produced by carbo-r thermal reduction methods, to tablet the dustand to use the tablets as resistors throu h which an electric currentmay be passed. The mag-;.

nesium vapors are then withdrawn from the mass of tablets throughopenings or slits in the heating chamber and thence to be conducted toexteriorly arranged condensing chambers which are maintained attemperatures proper for the condensation of the magnesium in liquidform. Such arrangements turned out to be quite impractical since thecondensation of magnesium in the liquid state is attended by greatdifiiculQ ties. Also such procedure is only applicable to thedistillation of metallic magnesium which has already been previouslyextracted and which can be evaporated at much lower vacuums, say

between 10 and 20 mm. absolute pressure, so

aluminum alloys. Also, it may be mentioned that the method of usingtablets as resistors to;

which reference has been made, is attended with great difiiculties,since in the larger types of,

equipment, irregular heat distribution takes place, and since all ofthese materials have a temperature coeiiicient of resistivity which re;duces with an increase in temperature, the current concentrates on suchzones of lower resist ance which therefore increase in temperature sothat any such preferred path for the current gives rise to veryirregular heat distribution.

It is also impractical to introduce any considerable amounts of tabletsdirectly from the open air into high vacuum equipment since thesetablets are all of a porous nature and contain occluded gases whichwould be liberated as they entered a high evacuated evaporation or re,-duction zone, and the vacuum would lower to such a degree that thereduction would stop. The continuous introduction of fresh material intoany process of this type would involve the utilization of very large andpowerful vacuum pumps.

In order to overcome the difficulties attending the introduction of rawmaterials, whether tableted or not, into a high vacuum chamber, the.present invention contemplates introducing the. materials first into apreheating chamber in which they are heated to such a temperature, undermoderate vacuum conditions, that no ac- 3 tual reduction or evaporationof magnesium takes place but all occluded gases are liberated from theraw materials to be reacted or treated. It is desirable that suchpreheating take place at a temperature at which the formation ofmagnesium vapors would just begin,- or at which magnesiumalreadypreviously produced would-start.

to evaporate. The vacuum applied is also only slightly different fromthe vacuum applied later.

for the actual reduction or distillation. Thetemperature and vacuumconditions applied accord-' ing to the invention will vary somewhat withthe reducing agent and raw material employed,

but in the specific example described; certainex-- emplary temperaturesand pressures will be mentioned in connection with the reducing agentscalcium carbide and ferro-silicon Suitabletem;

perature and pressure conditions will also be suggested in connectionwith the distillation of magnesium dust.

Again, in equipment at-present-in use for the:

thermal reduction of-- magnesium with calcium PatentsNos. 2,309,643,2,309,644 and 2,310,188,- to insert within the retort-a system ofshutters similar toVenetian blinds, through which the magnesium vaporscan-be withdrawn to a central cylindrical openspace, withouthaving topass through the mass of raw material charged into the retort.According. tothesystem forming the subject of the present invention,noexteriorly heatedretort is used, and furthermore the method of usingthe-tableted starting material as a resistor for theelectric current, isgenerallyavoidedor appliedto such a-degree that'theflowc of thecurrentis-well controlled Inaccomplishing this object; theinventioncontemplatesthe.

provisionof retorts in whichthe-retort wall itselfcomprises theresistant conductor forthe passage" of the electric current; Metalretorts, made of certain heat resistant steels, could possibly-beemployed but even thebest heat resisting alloys-at the high temperaturesused-may-become quite.-

soft-so that the structure might deform -or even collapse. Therefore, itis preferred that therebe used for the retort walls, materials ofhighelectric resistance and high melting points forexample carbon, graphite,or silicon carbide; Alternative forms of these heating chambers will bespecifically described in the presentspecification and it is understoodthat .the upper and lower portions of the retort wallslare connectedrespectively with the current supply so thatthe retort between thesepoints: is highly heated and the material to be reacted movesdownwardlyl by gravity within the heating chamber.

Other objects and features of novelty will be apparent from thefollowing speoifioationwhenread in connection with the accompanying.drawings in which certain embodiments of the invention are illustratedby way of example.

Inthe drawings Figs. 1A and 1B show vertically aligned portions of oneform of apparatus which may be employed in pursuing the invention, thedisclosure being somewhat schematic with conventional parts and devicesbeing indicated diagrammatically, and the structure being for the mostpart;shown in vertical section; v

Fig. 2 is a fragmentary enlarged view in side elevation of one form ofheating, reducing, or evaporating retort;

Figs. 3, 4, and 5 are views in fragmentary elevation, vertical section,and horizontal section, of an alternative form of retort which may beused in substitutionfor the one illustrated in Figs. 1B and 20f thedrawings; and

Figs. 6, '7; and 8*are diagrams of the automatic controls which areadapted to be actuated by the passage of the material past points at theinlet and discharge portions of the apparatus and also atan-intermediate transfer point, where the material passeslfrom thepretreatment chamber to the, retort Referring particularly to Figs. 1Aand i. the. drawings, it,.will .ba seen that they p retreat; mentportion of the apparatus designatedaA'JSg adapted to be superposedupon.theretormportion B, and above. the pretreating. section.A ,ai.lockrchamber charging section Cis disposed, Between the. pretreatment sectionA- andv the. retort. sec.-, tion -B there is disposed a dischargechamber; D which introduces the pretreated material intoza. lock hopperarrangement Ea. Finally; the-waste; material from the retort:B leavesthe apparatus through a discharge sectiomF.

The charging arrangement 0 comprises a hin or hopper -Il into which theraw materials,= ineluding the magnesiumcontaining compoundsand thereacting materials-,--are-adapted to-bee placed. For example, inwthereduction ofa magnesium-silicate with caleium-carbidey a proreducedmagnesiumsilicateore is -mixed with the stoichiometricamountof calciumcarbide and pressed'into tablets which are charged;-into-the binorhopper i l.- The material may be fed into the lock chamber- [2byopening the valve I3 Another valvelfi-may beopened todischarge: thematerialfrom the-lock chamber I 2"into thepretreatment chamber l5"which" comprises an elongated vertical" cylindrical chamber passing;centrally through the pretreatment installationm The lock chamber l2 maybe periodically sub, jected to vacuum from the line IT, a valve [8controlling the connection of the line IT with the vacuum line 19leadingtothe'yacuum pump, 29.1 The line l9 connects directly with thereheat-q ment chamber l5.

Surrounding the pretreatmentchamber l5 ;is,- the insulatedcasing 22having; an; annular; internal heating, chamber 23in which are disposed;an annular series of vertical resistorrods 2!; Conductor rings 25 aredisposed attire-upper and lower ends respectively-of theserodsand theserings are connected-toasuitable sourcex of heating current by meansofthe ,-lin e s ;2 5.5 The; resistors and the source ofcurrentgaremfsuchanature that a temperature of between ,900? and 9505 C.; may bemaintainedin the. heatingbhamber.

The lower end. of .thepretreatmentzchamber l5: extendsv beyond the.furnace- 22;: 23s and issurrounded by a.coolinghwater jacket.30 1wh'ichis suppliedcb'y the pipesr3ltandz32; Itmay= become necessary to cool thecharge -by-=means-oi= this 7 water. jacket. before. it enters. thehopper -con- 5"" necting the pro-treatment chamber I5 with the otherportions of the apparatus.

From the pretreatment chamber I5 the material passes into the dischargedevice D which consists of a hopper 33 in which a rotating disk 34 iscarried upon the end of a shaft 35 adapted to be driven by the motor 35through the bevel gears 31. A scraper element 38 cooperates with thedisk 34 and may be adjusted to control the discharge of material fromthe disk 34.

From the hopper 33 the pretreated material is passed through the valve40 into a lock or charging chamber 42, and from thence through the valve43 into a charging chute 44 which is introduced into the retort 45within the retort furnace B. By operating the valves 40 and 43, the lockchamber 42 may be alternately placed in communication with the vacuumsystem of the pretreatment chamber IE or that of the reducing ordistilling retort 45. The vacuum in the reduction retort system B ismaintained through a line 41 which leads to the high vacuum pump 50. Theother connections from this pump will be later described.

The retort chamber comprises the elongated cylindrical tube 45 which inthis embodiment consists of a tube of carbon provided with a spiral slit52 through which the magnesium vapors may pass into the surroundingchamber 55, the chamber 55 being lined with blocks or stones of carbonindicated at 56. Adjacent the upper end of the retort tube 45 is theannular water cooled contact ring 58, and a similar ring 59 is securedto the lower portion of the tube, both of these rings being connectedwith a suitable source of current by the leads 60 and GI.

Within the upper portion of the retort casing B and surrounding theupper portion of the retort tube 45 is the annular condensing chamber55, this chamber being provided with an inlet passageway 66 formagnesium vapors and a trough or gutter 6'! for cooling the condensedmagnesium. A conical flange 68 cooperates with the vertical flange 59 toprovide a narrow circular gas passageway I for admitting the vapors tothe condensing chamber 65. An inclined discharge duct I2 leads from thetrough 61 and this passageway i provided with a refractory or carbonplug 13 and a cover or closure I4 both of which are periodically tappedfrom the trough 61. adapted to be removed when the magnesium is Thecondensing chamber 65 is provided with a jacket I through which an airor gas stream can be circulated, this stream entering through the lineI0 and leaving through the line I'l, these lines being respectivelycontrolled by valves 18 and 19.

Heating means are provided for the condensing chamber 65 within theouter annular casing 80, this heating means comprising an annular seriesof resistor rods BI having rings 82 at the upper and lower ends, whichrings are connected with a source of current by the leads 83.

All of these chambers and retort passageways are enclosed within theinsulation 85 Which is in turn covered by the shell or outer wall 86which houses the entire retort system B.

A tubular lower extension 90 extendsfrom the lower end of the retorttube 45 exteriorly of the casing 86, and waste material is dischargedfrom the retort through this extension into the discharge mechanism Fwhich consists of the discharge hopper 9I in which a rotating disk 92 isprovided similar to the disk described in con-- nection with the hopper33 in the discharge are. rangement D. A scraper 93 is associated withthe disk and a motor 95 serves to rotate the disk through the gearing 96and the shaft 91.

As already indicated the vacuum line 41 leads from the condensingchamber 65 which is also in communication with the interior of theretort 45 and the surrounding chamber 55. The pipe 41 may be placed incommunication with the high vacuum pump 50 by means of the valve I00.The line may also be placed in communication with a source of supply ofa gas which is inert to magnesium, by means of the valve IM and the pipeline I02. Such gas may be hydrogen or one of the inert gases, argon,helium, or the like. A valve I04 in the line I05 serves to connect theintermediate lock chamber 42 with the vacuum pump 50.

A connection I06 is provided in the tube 44 which introduces thematerial into the retort 45, and a similar connection I0! communicateswith the discharge portion leading from the retort 45. A small quantityof an inert gas can be introduced through these lines during theoperation to prevent any condensation of magnesium vapors in the zoneswhere the raw material is charged and the waste withdrawn.

In Figs. 3, 4, and 5 of the drawings there is illustrated an alternativeform of retort which may be substituted for the tube 45. In thisembodiment the walls of the retort consist of an annular series ofvertically disposed rods IIO, these rods being made of carbon, graphite,silicon car-, bide or other resistant material. III are left between therods through which the magnesium vapors may escape. All of the rods III)are socketed as at H2 in the upper and lower annular rings H3 and H4,which rings are connected with a source of current by means of theconductors H5 and H5.

Of course the retort chamber may be varied still further, the rods I I0being arranged in either a circular form or in helical or rectangularconfiguration. The slits between the rods are of course small enough toretain the tablets and prevent their falling out into the surroundingchamber 55.

The surrounding insulating material 85 is selected so as to provide ajacket which is not too porous. The whole arrangement is placed withinthe jacket 86 which can be maintained at a temperature of approximately500 C, and if desired an outer jacket of porous or non-porous insulatingmaterial may be provided as suggest ed at 85 in Fig. 1B.

In cases where magnesium containing materials like powdered magnesiumoxide or magnesium silicate ores are to be reduced with cal-j ciumcarbide, the pretreatment zone within the chamber I 5 has to bemaintained at temperatures around 900 to 950 C. and at a vacuum of fromabout 1 to 2 mm. of mercury absolute pressure.

It is of course also possible to use a vacuum of between from 1 to 10mm. Under a vacuum of 1 mm. there may be some magnesium losses in thepretreatment stage, and on the other hand a vacuum of 10 mm. may notlead to a satisfactorily thorough degassing of the raw materials. Formixtures of dolomite with ferro-silicon, a pretreatment temperature offrom about 1050 to" The motor is of the variable speed type by meansNarrow spaces L100? 5G,;andla .vacuum. .of. between. 11 mm. andmm;;pressure-.is.:of advantage.

Themagnesium vapors condense; on the; sure; face'of thechamber. 65insolid form usually at a:.temperature range of 400 vand..60.0." C.

The. operation of' the installation may. be. efiected. entirelyautomatically or by manual control. In thelatter case theraw materials.and reducing agents in pellet form may be. placed in. the charging bin 1I. Then with the charging valive L L-closed, the valve l8closed so; asto. cut' off; the vacuum from the lock chamber. 52, and. the. valve. I8A opening the chamber to the atmosphere; the materialvalve i3. isopened and. the lock l2rfilled. Then the valve I3 is closed, the valve|18Ais closed, andlthe valve is. opened to vacuum. The valve It may.then be opened and the'imaterial discharged into the pretreatmentchamber l5. In the pretreatment chamber the material is heated bypassing through the zone which surrounded by the furnace 23; 2-9;;

.When the material from the pretreating installation A is to betransferred to the retort installation B, the material valve 33; the gasvalve I01, and vacuum valves Hit and HM are closed, the valve 29 isopened and the motor 36. starts the discharge mechanism Stoperating. Thepretreated'material is charged into the lock chamber or bin. 12 and thenthe motor 35 is stopped, the valve :ilLclosed, the vacuum valves I06.and I04 opened and then after operation vacuum has been reached thevalve 43' is opened so that the material can be charged into thereaction chamber 45.

When sufiicient material has been charged into the retort tube 45 it isheated to the reaction temperature approximately between 900 and 950 C.by means of current supplied through the leads 68 and iii to theconductor rings 58 and 59 atopposite ends of the resistant retort tube45. During the reduction or volatilization of a charge, cooling airisadmitted through'the valve 18 to the jacket '55 and exhausted throughthe outlet valve '59. This keeps the condensation chamber 65 at theproper temperature tocause the vaporized magnesium to condense on thewalls. At the same time valve W is maintained. open and the high vacuumpump 56 reduces the pressure Within the reaction chamher to the desireddegree.

After the deposit in the condensing chamber 65 has reached apredetermined thickness, the flow of material in the reduction chamberis stopped, the vacuum valves mo and 164. are closed, and the vacuum inthe portion of the system. including thecharging bin or look; 42,. thereaction chamber 45, the discharge hopper 9.1, and the waste bin 98 isreleased by opening. the valve I 0|, thus admitting a quantity of: inertgas. The air cooling of the condensing chamber 65 is stopped by shuttingoff the valves 18 and 19 and the current supplied through the. leads B3to the heater 8| is turned on so that the condensing chamber israised'to a tem.- perature at which the magnesium melts down from thewalls and runs into the gutter that portion of the magnesium whichhasvadhered to the inner wall of the chamber being;- guided into thegutter by means of the conical eaves 68. To discharge the moltenmagnesiumthe' cover 14 is removed from the outlet tube- 12*and theinserted carbon rod'orplug I3. is withdrawn and the magnesium tappedfrom the opening in liquid form. At thesame timethe;

chamber 98 through: therva ve; 9.9;. A t rrth st the rod 13 isreintroduced. into the: discharge, pine; 1.1L- the; vacuumtieht.cov 1 1n thesy mmlacc under v cuu a by; Qu e ing'valves; lflBand'iM' (of courseafter closing gasvalve L019, After full vacuum has. been, reached; the.discharge mechanism 92 is turned rr agam-.to..continue; the operation.

In .carryingout the process in a substantially; automatic way-,theopening and closing of the. valves; and. the connection; anddisconnection; of the ;vacuum,, pumps, can be effectedby remote;controlrelectrical or electronic devices or robotsff, It can-easily bedetermined by experimentjhow; much; magnesium afcertain volume oftablets; will producewhen a; certainraw material mix. ture, is-used.This ratio gives the relationship between; the volume accumulating inthe was te, chamber; 98' and the volume oi magnesium ac cumulating inthe condensing chamber- 65, level. controlled device 40! is arranged in:the, upper; portion. of the; waste receiving chamber; 93 -at-a pointwhere the waste representingone; charging 'of material will reach When,the; waste-material discharged by the rotating disk mechanismflz reachesthe level of the element. @flL controlling mechanism in the robot 3mlis-actuated. This mechanism is preferably electricalandthelevelindicator or level responsive element l01 ,may comprise any sort ofswitching device. whichwill be actuated by. the rising level. ofpulverulent. waste materiaL' The devices'dis'e, closed in United StatesPatents 1,578,563 1,951,980, and 1,977,228-are only a few examplesofdevices of; this kind which may be utilized',

Referring now to. Figure 8 of the drawings itwill be. seen. that theswitching mechanism in the robot 400 will serveto actuate the controllingmotors il i, 4.12, MB, etc. to controlthe'f several. valves andmotorsfas'will now be de-'-. soribedl' The. actuating or controllingmotors. 411,412,413, etc. are connected with the, master; controllingdevice or robot 400 by means of thefpairs of conductors 420, and upon.actuation. oifthe'l'ev'el responsive element Mi," current is supplied tothe motor 4'! l which is connec'te'df' with the material introducingvalve 43' as' by. means of'the shaft Ml to turn this valve on; if-"itis; on and" to; keep it turned on" if it has; already been turned off byother controls. Similarly the motor- 4l-2 acts throughacorrespondingshaft 421- to turn the vacuum valve Hit-off; Themotor 41-3is actuated toturn the vacuum valve H34 off, which will disconnect theleck ilfrom the vacuum pump 50. Motor 4 14 turns .thevalve Hill on, thusadmitting inert gas to the retort and condensing, system: This. sameactuation of the level responsive member. tilt. turns the motor 95 offand stops the delivery mechanism 92, Similarly the motor 4E5 serves; toturn the cooling; air admitting valve [8 our and at the same timetheheating elementssup.- plied through the leads 8.3-are turned on tostart: the melting of the depositedmagnesium.

The time necessary to melt down, the magnesium can 'be easilydetermined.experimentally,: and the. timing mechanism 4|! can beadjusted; so as to give a signal such as a visual signaleaf-ij forded.by the. light M8 which when: observedv by the operatorwill indicate tohim that it isg timeto removev the cover 1-4 and-I the plug. 13: and tapthe magnesium, andalso to open the; discharge valve 99; to empty thecontainer 93;.

In order to ;keep. the charging bin 42 indejwaste material may; bewithdrawn from the. 1 pendently, filled. with pretreated rawma-terials;

a second controlling device or robot 300 is provided. This controllerhas one section 300A adapted to be energized by a high level responsiveelement 30I and another section 300B to be energized by the low levelcontrol device 302. These elements 30I and 302 are connectedrespectively to the control devices by the conductors 303 and 304. Whenthematerial dis-- charged into the retort through the valve 43 reachesthe low level 302, the device 300B is energized to close the valves 43and I04, open the valve 40 and start the motor 36 for operating thedischarge mechanism 34. Then the pretreated raw material is charged intothe hopper or lock chamber '52 until the level 30I is reached. At thispoint the high level control portion 300A of the mechanism 300 isenergized to close the valve 40, shut off the delivery motor 36, and ifthe lowermost system of controls centered about robot 400 permitsit,open the valves 43 and I04. It will be noted that in the conductor line320 leading to the motor 3I2 which controls the valve 43 there isdisposed a vacuum gage which delays the energizing of the motor 3I2until operation vacuum has been reached. The several valves 'anddischarge mechanisms are adapted to be actuated by the indicated motors3I I, 3I2, 3I3, etc., through the shafts 32I.

In a similar fashion, a third electrical or electronic controller 200 isemployed to control the initial charging mechanism C. This devicecomprises a high level control portion 200A adapted to be activatedthrough the conductor 203 from the high level responsive element MI anda low level control portion 200B energized by the low level responsiveelement 202. When the low level responsive element 202 is actuated, thecontrol 200B is energized to actuate the appropriate motors to open thevalve I3, to close the valve I4, to close thevacuum valve I8, and toopen the valve I8A venting the chamber I2 to the atmosphere. After thelock chamber I2 has been filled to the level 20I, the high level control200A is energized to turn the valve I3 off,

to turn the valve I4 on, to turn the vacuum valve I8 on, and to closethe valve ISA leading to the atmosphere. The operation of valve I4 isdependent upon the attainment of the necessary operating vacuum, and forthis purpose the vacuum gage 205 is interposed in the line 220 leadingto the motor 2I2 which actuates this valve.

Thus it will be seen that with such automatically controlled devices, itis possible to maintain the correct operation of this installation withvery few workers.

It is understood'that various changes and modifications may be made inthe embodiments illustrated and described herein without depart" ingfrom the scope of the invention as defined in the following claims.

Having thus described the invention what is claimed as new and desiredto be secured by Letters Patent is:

1. A continuous process for the recovery of metallic magnesium, which isapplicable to the thermal reduction method involving non-carbothermalreduction of magnesium and which will not evolve gaseous products, andto the evapora tion of magnesium contained in the dust produced bythermal reduction methods; which process comprises establishing twoconsecutive treatment zones under separate vacuum conditions, the

tion of magnesiumf'feeding successive charges of raw material throughthe I pretreatment zone and thence into the second named zone without"exposure to the atmosphere or substantial loss of vacuum in eitherzone; heating the charges while in said pretreatment zone at suchelevated temperatures under such vacuum conditions that only a slightevolution of magnesium vapors begins to take place andany occluded gasesare removed; heating said charges after they have been moved-to thesecond named zone to a high temperature under vacuum conditions toevolve magnesium vapor; and condensing said vapor.

2. A continuous process for the recovery of metallic magnesium, which isapplicable to the thermal reduction method involving non-carbothermalreduction of magnesium and which will not evolve gaseous products, andto the evaporation of magnesium contained in the dust produced bythermal reduction-methods; which process comprises establishing twoconsecutive treatment zones under separate vacuum conditions, the firstfor pretreatment'and the' second for evolution of magnesium; feedingsuccessive charges *of raw material through the pretreatment zone andthence into the-second named zone without exposure to the atmosphere orsubstantial loss of vacuum in either zone; heating the charges in saidpretreatment zone at such elevated temperatures under such vacuumconditions that-only a slight evolution of magnesium vapors begins totake-place and any occluded gases are removed; reducing the temperature.of said charges before moving them from said pretreatment zone, asforthepurpose of preventing injury to parts oflthe apparatus used;heating said charges after they have been moved to the second named,zone to a high temperature under vacuum conditions toevolve magnesiumvapor, and condensing said vapor. I I

3. A continuous process ,forthe recovery. of metallic magnesium, whichis applicable to the thermal reduction method involving non-carbothermalreduction of magnesium and which will not evolve gaseous products; whichprocess comprises establishing two consecutive treatment zones underseparate vacuum conditions, the first for pretreatment and the secondfor reaction; feeding successive charges of raw material through thepretreatment zone and thence into the reaction zone without exposure tothe atmosphere or substantial loss of vacuum in either zone; heating thecharges in said pretreatment zone at a temperature of from about 900 C.to about 1100 C. and under a vacuum of from about 10 mm. to about 1 mm.,whereby only a slight evolution of magnesium vapors begins to take placeand any occluded gases are removed; reducing the temperature of saidcharges before moving them from said pretreatment zone, as for thepurpose of preventing injury to parts of the apparatus used; heatingsaid charges after they been moved to the reaction zone at a temperatureof from about 1100 C. to about 1300 C. and under a vacuum of from about1 mm. to about 0.1 mm. to evolve magnesium vapor; and condensing saidvapor.

4. A continuous process for the recovery of metallic magnesium, which isapplicable to the evaporation of magnesium contained in the dustproduced by thermal reduction methods; which process comprisesestablishing two consecutive treatment zones under separate vacuumconditions, the first for pretreatment and the second first forpretreatment and the second for evolufor vap ration of ma nesium; feedinsu s- "sive charges of raw material'through the pretreatment zone andthence into the evaporation zone without exposureto the atmosphere orsubstantial loss of vacuum either zone; heating the chargesin-saidpretreatment zone at a temperature of from about 600C. to about750 C. and under a vacuum of'from about 10 mm. to about 1 mm., wherebyonly a slight evolution of magnesium vapors begins to take place and any"occluded gases areremoved; reducing .the temperature of said chargesbefore 'moving them from said pretreatment zone, as for the purpose ofpreventing injury to partso'f the apparatus used; heating saidcharges-after they have been moved to the evaporation zone to atemperature "of from about 600? C. toabout 750 C. and under a vacuum offrom about 1 mm. to about 0.1 mm. to evolve magnesium vapor;and-condensing said vapor.

5. A. continuous process for the recovery of metallic magnesium,which-is applicable to the thermal reduction method involvingnon-carbothermal reduction of magnesium and which will not evolvegaseous products'and to the evaporation of ma nesium contained in thedust pro duced by thermal reduction methods; which process comprisesestablishing two consecutive treatmentzones under separate vacuumconditions, the first for pretreatment and the second for evolution ofmagnesium; feeding successive charges of raw material through thepretreatment zone andthence. into the second named zone without exposureto the atmosphere orsubstantial loss of vacuum in either zone; heatingthe charges 'in said pretreatment zone at such elevated temperatures.under such vacuum conditions that only a slight evolution of magnesiumvapors begins to take place and any occluded gases are removed; reducingthe temperature of .said charges before. moving, them to said secondnamed zone, as forthepurpose of preventing injury topartsof theapparatus used; heating said charges after they have beenmoved to thesecond named zone to'a high temperature under vacuum conditions toevolve magnesium vapor, and condensing said vapor.

6. A continuous process for the recovery of metallic magnesium, whichisapplicable to the about 1100 C. and under a vacuum of from about 10 mm.to about 1 mm., whereby only a slightevolution of magnesium vaporsbegins to take place and any occluded gases are removed: heating saidcharges after they have been moved to the reaction zone at a temperatureof from about 1100 C. to about 1300 C. and under a vacuum ofirom about 1mm. to about 0.1 mm. to evolve magnesium vapor; and condensing saidvapor.

FRITZ J. HANSGIRG.

REFERENCES CITED 7 The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name 'Date 2,011,288 Kemmer Aug. 13, 19352,219,059 Suchy et al Oct. 22, 1940 2,258,374 Amati Oct. '7, 19412,310,188 Hansgirg Feb. 2, 1943 2,362,718 Pidgeon Nov. 14, 19442,391,156 Hansgirg Dec. 18, 1945 2,391,193 Rademaker Dec. 18, 19452,430,389 Chubb Nov. 4, 1947

1. A CONTINUOUS PROCESS FOR THE RECOVERY OF METALLIC MAGNESIUM WHICH ISAPPLICABLE TO THE THERMAL REDUCTION METHOD INVOLVING NON-CARBOTHERMALREDUCTION OF MAGNESIUM AND WHICH WILL NOT EVOLVE GASEOUS PRODUCTS, ANDTO THE EVAPORATION OF MAGNESIUM CONTAINED IN THE DUST PRODUCED BYTHERMAL REDUCTION METHODS; WHICH PROCESS COMPRISES ESTABLISHING TWOCONDUCTIVE TREATMENT ZONES UNDER SEPARATE VACUUM CONDITIONS, THE FIRSTFOR PRETREATMENT AND THE SECOND FOR EVOLUTION OF MAGNESIUM; FEEDINGSUCCESSIVE CHARGES OF RAW MATERIAL THROUGH THE PRETREATMENT ZONE ANDTHENCE INTO THE SECOND NAMED ZONE WITHOUT EXPOSURE TO THE ATMOSPHERE ORSUBSTANTIAL LOSS OF VACUUM IN THE EITHER ZONE; HEATING THE CHARGES